The present invention relates to a method for structured energy transmission by transmitting for short periods energy using electron beams to limited surface elements of, preferably, plane surfaces of objectsxe2x80x94such as parts, plates or bands of metallic, semi-conductive or dielectric materials or combinations of such. The useful processing effects are determined by the physical or chemical reactions of the materials to the energy transmission by means of electron beams. The preferred field of application is the structuring of surfaces on strip-shaped objects of any length by means of a limited number of repeated structural elements which are matrix-like arranged in columns and lines.
It is general knowledge how to use electron beams in a large variety of ways to respectively process materials or change material properties. In the main, probe- and mask-type processes are applied to generate surface structures.
Probe methods are characterised by the application of a focused electron beam which, according to the structural elements to be generated, affects the object by programmed beam deflection, which is known per se. With this method energy is transmitted to the different surface spots in a certain time sequence. The application of this method is extraordinarily flexible. However, its disadvantage is that it cannot generate structural elements whose lateral expansion is smaller than the diameter of the electron beam focal spot. Frequently, it is also not possible to place too high demands to the homogeneity of the energy density to be transmitted per surface unit within the structural elements. Although this method allows for a homogeneity improvement by reducing the focal point diameter via the modification of the optoelectronic focusing conditions, the adverse consequence is a reduction of the usable beam deflection amplitude. Then larger surfaces are processed by means of time-consuming mechanical shifting of the object, e.g. with the step-and-repeat technique. One limitation of the application of the probe method is particularly the structuring of large surfaces with densely located small structural elements, where the technically limited beam deflection velocity of the electron beam is able to extend the processing duration for a certain task till well into the range of the inefficiency of the processing method. In addition, when thermal processing effects are used, the probe method is often not able to meet the demand for a sufficient simultaneity of energy transmission to the entire structural element.
The structured energy transmission according to the mask method applies different task-specific variantsxe2x80x94predominantly in electron beam lithography, where the optoelectronic imaging of a template, which illuminates the structural elements as recesses by the electron beam, has gained a certain significance. Combination techniques are also known, characterised by the optoelectronic imaging of a template which contains the structural elements and the latter""s positioning on the object as defined by an additional beam deflection. The disadvantages of these techniques are their high apparatus requirements and the low values of the momentarily transmittable energy density. Hence, their practical application is restricted to electron beam lithography for the generation of latent structures in the micron and sub-micron range.
The invention is based on the task of developing a method for structured energy transmission to an object surface by means of electron beams which gets past the limitations of the prior art methods. Thus it shall be possible to impinge upon minuscule surface sections, e.g. pixels, using an electron beam with a given arrangement on the surface in order to achieve certain processing effects. In particular, it shall permit a defined variability of the transmitted energy density for a limited number of different structural elements. Non-thermal and thermal processing effects shall be achievable with a high productivity and a high quality.
According to the invention the task is solved according to the definitions of patent claim. Further advantageous embodiments are described in patent claims 2 to 11.
Essentially, the solution according to the invention is provided in that an electron beam is high-frequency deflected in the known way into one directionxe2x80x94the oscillation directionxe2x80x94according to a periodic function and, nearly perpendicular to the oscillation directionxe2x80x94in deflection direction -, is made to act using beam deflection via the recesses in a mask onto the surface of an object which is moved contact-free under the mask in the oscillation direction. The motion speed of the electron beam in the deflection direction is high compared to the speed of movement of the object. The energy is transmitted to the object surface sections, which are defined by the lateral expansion of the mask recesses, in several partial amounts that are determined by the frequency of the periodic deflection function, the speed of the beam deflection in the deflection direction, the beam diameter in the mask plane and the lateral expansion of the mask recesses. If there is a high demand to the homogeneity of the energy density the three first-mentioned influencing variables shall be matched. Most application require a constant energy density in at least one structural element, in which case it is suitable to use a known trigonometric function for the periodic beam deflection.
When carrying out thermal processing methods it is necessary to transmit the required energy density within a short period of time in order to achieve a quasi-adiabatic energy transmission, i.e. without any essential heat dissipation from the energy-absorbing material volume during the energy transmission period. Particularly in this case the electron beam is focused into the mask plane and the periodic deflection kept as high as technically possible, e.g. in the range between 100 kHz and 1000 kHz. The beam deflection speed into the deflection direction is rated sufficiently high so that the energy transmission period, which results from the ratio between the beam diameter in the mask plane and the beam deflection speed, meets the demands to a sufficient adiabatic beam deflection speed. The impact on the processing effect of the exact transmission of the periodic deflection function, which is hardly implementable in this case, is limited in the mirror points by choosing the amplitude larger by a number of beam diameters than the width of the recess sections in the mask.
If the structuring of an object requires energy densities that slightly vary locally, their adapted selection is suitably made by choosing an appropriate amplitude of the periodic deflection function.
If the structural elements are arranged matrix-like on the object, it is suitable to choose the two deflection directions nearly perpendicularly to each other according to the structural arrangement on the object.
If all structural elements shall be impinged with about the same energy density it is suitable to keep the beam deflection speed constant in the mask deflection direction. While in case of a high variation of the energy density it may advantageous to perform the matching by means of a position-depending deflection speed into the deflection direction.
During thermal processing methods the thermal loadability of the mask may limit the method. In such case it is advantageous to manufacture the mask of material with good heat-conducting and temperature-resistant properties and to design a water cooling system directly adjacent to the recess section. Here, the mask recesses are restricted to a gap. The parallel arrangement of a number of such gaps in the mask, through which the electron beam travels cyclically one after the other, can considerably increase the thermal loadability of the mask. Such arrangement of gaps in the mask can also be advantageous when structural elements, which are located on the object closely to each other in the direction of the gap, shall be impinged with differing energy densities.
In order to achieve a high process productivity it is advantageous to move the object to be processed under the mask perpendicularly to the deflection direction and at a constant speed. High demands to the rectangularity of the processing structure on the object can be met under these conditions by turning the mask towards the structure on the objectxe2x80x94at constant beam deflection speed into the deflection directionxe2x80x94in such a way that the impact of the operating time effect on the position of the surface elements on the object which are impinged by the electron beam is eliminated by the finite beam deflection speed into the deflection direction.
The process according to the invention can be particularly advantageously applied when strip- or band-shaped objects, whose width is within the implementable beam deflection amplitude in the deflection direction, shall be processed in a structured way. In case that the object width exceeds these limits it is possible to impinge the entire object surface by combining strip-shaped partial surfaces.
One advantageous application area is the highly efficient structured processing of objects with a relatively large surface. In the sphere of non-thermal electron beam processing this applies predominantly to the structured modification of plastic materials, the creation of colour patterns in materials filled with suited electron-beam-sensitive dyes.
In the sphere of thermal electron beam processing the process can be applied both in the optical structuring of suitably sensitised glass surfaces in order to generate displays and in the structured hardening of metal surfaces from hardenable materials or for abrasive processing, e.g. of plastics by means of material evaporation.
The preferred area of application of the process are plane strip- or band-shaped objects, although also curved surface can be processed, e.g. cylindrical objects, where, if need be, the mask shall be matched to the object shape.